The dark side, I heard they have cookies

The battle of good vs evil never ends; there is always a Lex Luthor or Joker that comes in the way of our superman or batman. The archetypal good guy vs bad guy plot has been around since the beginning of literature. Though the passage of time clumped many morals and values onto the the two, when all of the fluff associated with them are removed, when they're striped down to the most basic definitions, there is a rather fundamental theme that both define themselves by. An action that helps others is considered "good"; an action that harms others is considered "evil". In other words, it doesn't matter what you does to yourself, the evaluation of good and evil relies solely on the effects on other people.

In order to better understand the two, it's important to look at its embodiment in real life. Lets say in this scenario, there are two kings, King A and King B. King A is caring to his people and rules to ensure their happiness. The people enjoy happy lives under his rule and the idea of good attaches itself to the king. King B is a tyrant who only wants power and do so at the cost of the people. King B's people live in poverty, and in turn they consider the king to be evil.

The concept of good and evil guide civilizations to strive on the basis that people should be "good" and help each other out, thus promoting contributions to society as a whole. At the same time, laws are created to prohibit "evil" actions that harm society. It can be safe to say that King A's empire will be more prosperous and powerful than King B's, because King A ruled in accordance with the idea of "good" and cared about the welfare of others. Perhaps the two sides of the spectrum were created by man, or maybe were already a part of human consciousness. Either way, the two are a natural protection that steer people to put the good of the many over the good of oneself.